The mass transfer equations account for chemical species transport by diffusion, convection, and migration due to an electric field (electrokinetic flow)—either alone or in combination. The Transport of Diluted Species Interface (
) is an enhanced version of the physics interface included with the basic COMSOL Multiphysics license and is applicable for solutions (either fluid or solid) where the transported species have concentrations at least one order of magnitude less than the solvent. The settings for this physics interface can be chosen so as to simulate chemical species transport through diffusion (Fick’s law), convection (when coupled to fluid flow), and migration (when coupled to an electric field — electrokinetic flow). Also see the
The Transport of Diluted Species Interface.
The Transport of Diluted Species in Porous Media Interface (
) is tailored for the modeling of solute transport in porous media. The physics interface supports cases where either the solid phase substrate is exclusively immobile, or when a gas-filling medium is also assumed to be immobile. Also see the
Mass Balance Equation for Transport of Diluted Species in Porous Media.
The Transport of Concentrated Species Interface (
) is used for modeling transport in gas or liquid mixtures where no component is clearly dominant. Often the concentrations of the participating species are of the same order of magnitude, and the molecular effects of respective species on each other needs to be considered. This physics interface supports transport through Fickian diffusion, a mixture-average diffusion model, and as described by the Maxwell-Stefan equations. These take into account the diffusion properties of all species with respect to each other. Convective transport and transport by migration in electric fields are also accounted for by this physics interface. Also see the
Theory for the Transport of Concentrated Species Interface.
The Transport of Concentrated Species in Porous Media Interface (
) is tailored for the modeling of gas or liquids mixtures in porous media.
The Nernst–Planck Equations Interface (
) is used to compute concentrations in electrolytes subjected to electric fields. It defines the material balances and transport of ions and neutral species in combination with the electroneutrality condition. The physics interface can be used to model generic electrochemical cells with significant concentration gradients of the current-carrying species (ions). Also see the
Theory for the Nernst–Planck Equations Interface.
The Nernst–Planck–Poisson Equations Interface (
) describes transport of electrolyte species without assuming local electroneutrality. This allows for simulating charge separation that typically arises close to an electrode surface, where ions in the electrolyte are attracted and repelled by unscreened excess charge on the electrode.
The Electrophoretic Transport Interface (
) is used to compute the potential and concentration fields of a dilute solute in an aqueous solvent. The interface combines the Nernst–Planck equations, with electroneutrality and dissociation equilibria for weak acids, bases, and ampholytes, as well as the water auto-ionization reaction. It can be used to model various electrophoresis modes, such as zone electrophoresis, isotachophoresis, isoelectric focusing, and moving boundary electrophoresis. Also see the
Theory for the Electrophoretic Transport Interface
The Chemical Species Transport >
Reacting Flow branch contains multiphysics interface that combines the equations for fluid flow with equations governing mass transport and reactions in fluid mixtures. Multiphysics interfaces for diluted solutions, as well as for concentrated solutions are available. The physics interfaces support laminar flow and, depending on the licensed products, turbulent flow.
The Chemical Species Transport >
Reacting Flow in Porous Media branch contains multiphysics interfaces that combine equations for fluid flow and chemical composition of a gas or liquid moving through the interstices of a porous medium. The branch also included dedicated interfaces for modeling porous catalysts and packed bed reactors. Apart from porous media, the system may also include regions with free flow.
The Chemical Species Transport >
Nonisothermal Reacting Flow branch contains multiphysics interface that combines the equations for fluid flow, heat transfer, and mass transport and reactions in fluid mixtures. These physics interfaces support laminar flow and, depending on the licensed products, turbulent flow, as well as flow through porous media.
The Dispersed Two-Phase Laminar Flow with Species Transport Interface (
) can be used to simulate species transport in a two-phase flow involving a liquid and a dispersed phase consisting of bubbles or droplets. Transport and reactions in both phases as well as transfer between them can be studied.
The Vapor–Liquid Equilibrium multiphysics interfaces can be used to model vapor transport in multicomponent mixtures in contact with liquids. The Laminar Vapor Flow (
) version includes features for evaporation and condensation at vapor–liquid interfaces. The
Laminar Two-Phase Flow (
) version can be used to also track the motion of the interface resulting from the mass transfer.
The Precipitation and Crystallization in Fluid Flow Interface (
) can be used to model the size distribution of particles or that precipitate out of a fluid solution. It can be for example be used to study crystals in a liquid, gas bubbles in a liquid, or droplets in a gas.
The Size-Based Population Balance Interface included solves for the discretized size distribution of particles, with support for growth and nucleation terms.
The Surface Reactions Interface (
) models reactions involving surface adsorbed species and species in the bulk of a reacting surface. The physics interface is typically active on a model boundary and is coupled to a mass transport physics interface active on a model domain. The Surface Reactions interface can be used together with other Chemical Species Transport interfaces. Predefined expressions for the growth velocity of the reacting surface makes it easy to set up models with moving boundaries. Also see the
Theory for the Surface Reactions Interface.
The Transport of Diluted Species in Fractures Interface (
) is used to model transport of a solute species along thin porous fractures, by accounting for convection, diffusion, dispersion, and chemical reactions. The fractures are defined by boundaries in 2D and 3D. The mass transport equation solved along the fractures is the tangential differential form of the convection–diffusion–reaction equation.